Add option to display a group's members divided by role

[Thomas Niebler]

On the groupsettings page, it would be a nice feature to have different view options for the member list, such as

• provide separate lists for user roles
• sort users by name/user role/join date
• mark the group user (if present) in a special color?

[Mario Holtmüller]

resolved.

I implemented ONE list list that can be sorted by name, role and join date.

I skipped the part with marking the group user, as it cannot be present?!